Document 0JX2D0933BjJg7QBRMY4E0qok

10/08/2001 15:58 312-996-7822 SCIENCE LIBRARY tNVlKQNMCNTAL 16, J83 ~ 397 (1978) On the Utility of Dark-Field Electron Microscopy in the Determination of the Degree of Deformation In Chrysotile Asbestos'. An Environmental Research Application K. SlSHAN Department of Materials Science ond Engineering, Materials and Molecular Research Division, Lawrence Berkeley Laboratory. University of California, Berkeley. California 94720 Received June 71, 1977 Tbc degree of microcryileliiat defornwtico in liber* of chrysotile s*bc*to* may be dUlinuiabed wine hi(h re*oLnion dark-field electron nucrwcopy, Tbit i demonstrwed by com paring underonned chrytotik with Union Internationale Centre )c Cancer (UlCC) itandard reference sample*. The UlCC cample* are tbown to be partially deformed a* mult of milling in the raiding procct*- Sample* of u*cd and unu*cd brake ahoe lining dmt were examined wing tbi* technique; it i* tbown that chrytotile a*bettor in vanout *uge* of deformation--relatively undcformed to heavily deformed--turvivea in automobile brake drum dwt. Such dark-field image* can serve to identify the aource of aabeuot found in environmental pollution sample*. ' INTRODUCTION There is a controversy in the literature whether or not fibers of chrysotile asbestos survive in automobile brake drum dust; two studies (Rohl et at,, 1976; Aisle et at., 1976) report that the fibers do survive and earlier work (Lynch, 1968; Hickisb and Knight, 1970) reports that they do not. The latter claim that the chrysotile is converted to forstcrite under the high temperatures attained in the braking process. As high resolution dark-field electron microscope images are sensitive to the degree of deformation, they can be used to distinguish between deformed and undeformed fibers and thus to resolve these two differing sets of results. It is shown using this technique that chrysotile asbestos fibers in various states of deformation--relatively undamaged to heavily deformed and recrystallized--exist in automobile brake drum dust. SAMPLE SELECTION AND PREPARATION Four samples were selected: (A) undcformed chrysotile ore samples from ser pentine outcrops of Calaveras County (California); (B) slightly deformed UlCC reference standards of Canadian chrysotile milled during preparation to reduce fiber size (Timbrell et at., 1969); (Q unused brake lining dust, collected during burnishing prior to installation of new brake shoes; and (D) brake drum dust collected from the from and rear brake drums of a State vehicle obtained during brake shoe service (Seshan and Smith, 1977). Samples were transferred directly to Formvar-coated electron microscope grids and coated with carbon on both sides. 000-9351/78/16 J 3-O303SO2.OWO Opyrigftt 1919 Ac%fank Hr*!, Cue. All of rtp*?ductto* id iy form SCF-FA-7252 PAGE 03 10/'08/2001 15:58 312-996-7822 SCIENCE LIBRARY PAGE 04 384 K- SESHAN EXPERIMENTAL As the high resolution dark field method is described in great detail elsewhere (Hirsch et al., 1969), only a very brief description is included here. An electron beam striking a polycrystalline specimen with grains of different orientation (e.g., A and B in Fig. 1) is diffracted into cones, causing the typical polycrystalline ring pattern. The high-resolution dark-field method consists of tilting the incident beam so that the part of the diffracted ring passes through the optic axis of the micro scope (Fig. lb). The tilting is accomplished with the electronic beam tilt device. Then an aperture collects intensity only from those crystallites diffracting into this part of the ring, e.g., B (Fig. 1c). Various factors involved in the interpretation of the diffraction patterns of chrysotile asbestos fiber bundles are shown in Fig. 2. The actual lattice of chrysolite is a defected, scrolled crystal with fiber axis along a (Yada, 1967). The reciprocal lattice of this crystal should be some form of a spiral, equispaced along the a* axis. Zvyagin (1967) and Whittaker (1966) have studied diffraction effects from concentric cylinders. How deformation and shear will affect the diffraction patterns has not, to the author's knowledge, been studied and is under study here. The simpler case of an uodeformed defect-free chrysotile fiber, where the fiber is idealized as a series of concentric cylinders, as first proposed by Whittaker (1969), is shown in Fig. 2i. The reciprocal lattice then consists of a series of concentric rings, shown in Fig. 2ii (only the two rings in the 2ki layer are drawn). The electron diffraction pattern represents the intersection of the reflecting or Ewald sphere (ES, Fig. 2ii) with these rings (Hirsch et al., 1969). This ought to result in a series of spots as shown in the -2k! layer line, Streaked patterns are, however, obtained from single fibers of chrysotile (Yada, 1967; Seshan and Smith, 1977). The explanation for the streaking probably lies in refraction effects and the fiber shape (Yada, 1969); it could also result from the various faults produced during the l t Fic. 1. Illustration of- the high resolution dark-fold method', (a) The bright-held image from a selected area ofa polycrystal, illustrated with two grains, A and B (b) The situation alter gun tilt; only a portion of the diffracted intensity is collected by placing the objective aperture as shown, (c) The resulting high-resolution dark-fold image with only favorably oriented grains, e.g., B showing difftacted intensity or "lighting up," 10/108/2001 15:58 312-998-7822 SCIENCE LIBRARY DEFORMATION OF CHRYSOTILE ASBESTOS 383 PAGE 05 t m r I I I I I , ii t I ii I I* ti I I tl 1*1 OH -Af -t*t tv rf '' >\ V >. / J Fc. Z- Ulmtntton of Uw real and reciprocal lattice of a defect-fiee chrytotile fiber (1) and (U) idealised a* a aeriea of coocentric cylinder*- The actual structure i* a defected tpiral ebeet (Yada, 19(7). The reciprocal lattice of the ideal fiber w then a aerie* of eqvitpaccd concentric ring* along the a* axit, at in the Jkl layer, when tbete ring* Interteet, the Ewald sphere (BS) spots ought to be produced as shown on the -2kJ layer line. However, streaks are observed (Yada, 19(7), arising piste bly from the spiral shape of the fiber defect* and (trains formed during the *crolling process. When a fiber bundle (fiber* of different orientation*) is imaged, the layer line* are *mearcd out, yielding a typical "arcuate" pattern as In Fig. 3b. growth of the crystal. The influence of these faults on the diffraction patterns and their influence on deformation needs further study - When bundles of fibers are involved, the streaks are replaced by arcs (Pigs. 2iv and 3b), showing a strong tendency toward a texture and yielding the typical "arcuate" patterns observed by several researchers (e.g., Rohi el al., 1976), The dark-field image obtained by imaging any part of the arc, as sbowii in Figs, 1 and 3b, should yield uniform intensity, if the crystal is homogeneous. This is the case to be expected only in the case of the undeformed fibers--and is consistent with the experimental observations in Figs. 3a and 3b. RESULTS Bright- and dark-field images of naturally occurring chrysotile (A) are shown in Fig. 3, The dark field is obtained by imaging a portion of the diffiracted intensity, as explained above. The result is a uniform contrast, as would be expected from an undeformed crystal. The striking feature of the dark-field images is the great intensity along the hollow canals and this needs fiuther investigation. The intensity difference cannot be explained on the basis of differences in absorption alone; it appears that some 10/68/2001 15:58 312-996-7822 SCIENCE LIBRARY PAGE 06 F<c. 3. Sample (A): natwsJ chryxotile. () rad (b) Dwk-fietd rad diffraction pattern- Notice the unusually bright rad undamaged internal canalt; the crystal it homogeneous and undeformed- A faint outline of the objective aperture is seen in the diffraction pattern of Fig. 3b. (c) Illustrates the Mistering as a result of exposure to the beam. diffraction processes are operative: Notice that the canals are sometimes bright and sometimes dark. In the crystalline part, however, the intensity is uniform and it is clear that these fibers are free of gross deformation. Chrysolite fibers, like most sheet silicates, are beam-sensitive to 100-keV elec trons (Langer el al.r 1974; Seshan. 1975). Precaution must therefore be exercised while obtaining the high resolution dark-field images, because upon focusing the I 10/138/2001 15;58 312-996-7822 SCIENCE IIBRARV DEFORMATION OF CHRYSOTILe ASBESTOS 387 condenser, the fibers tend to become blistered. In the dark-field image shown in Fig. 3a, precaution was taken to prevent any beam damage; the condenser was not focused, and the beam was lilted in the dark field mode. The condenser was then PAGE 07 _ ft V" F/c. 4. Sample (8): UlCC Standard Reference Canadian chrysolite, (a) and (b) Dork-field image* that illustrate that the ball milling during the mixing step convert* the chrysolite into a fine-grained polycrystal. The aperture is moved from one part of the ring to another, resulting in an entirely different set of grains lighting up. <c) The bright-ficld image from which little information can be obtained. 388 K. SESHAN focused to obtain the diffraction pattern shown in Fig. 3b. The resulting beam damage is shown in Fig. 3c. The use of beam sensitivity to distinguish chrysolite from other non-beam-sensitive materials, e g., the amphiboles, has been dis cussed by Langere/ al. (1974). Dark- and bright-field images of deformed UICC standards (B) are shown in Figs. 4a-4c). The effects of deformation are clearly seen in the dark-field images (4a and 4b) and in the electron diffraction patterns but not in the bright-field Fie. 5. Sample (C) Bumithing <juit from an automobile brake drum prior to installation. (a) Dark field, (b) diffraction pattern, and (c) bright field. Notice the well-preaerved canal which shows up (the dark-field image) in (a), indicated by the arrow and arrowhead. This and the well-preserved diffraction pattern (h) show* that the fiber* are not as deformed a* the UICC sample*-- conclusion that cannot be inferred from the height-field image (c). 80 3Dtfd Ayyaan 30N3ids 228Z-966-2IE 8S:si 1002/80/01 10/08/2001 15:58 312-996-7822 SCIENCE LIBRARY DEFORMATION Or CHKVSOTIJLX ASBESTOS 389 images (4c). The clear internal canals of the undeformed sample (A) are destroyed; there appear small subroicron (100 A) areas which light up as if they were grains or microdomains of different orientations; consistent with this observation, the strongly textured diffraction patterns of the undeformed fibers (Fig- 3) are changed to those of a polycrystal- At the present the crystallographic and microstructural nature of the deformation is not clear and warrants further study. The effect of translating the aperture to a different part of the diffracted ring is shown in Figs. 4a and 4b- The result is that "grains" in a different orientation "light up" or show diffracted intensity signifying that this is truly a diffraction effect. To isolate the effects of deformation during the braking process, unused brake shoe burnishing dust (C) was examined (Figs. Sa and 5b). The bright-field image (B) is not informative, whereas the dark-field image clearly shows some intact internal canals (see arrow and arrowhead Fig. 5a) resembling the undeformed PAGE 09 Fic. 6, Sample (D); Brake drum dust after use in a state vehicle, (a) Bright field and (b) dark field. Although the bright field is not distinctive, (he high-resolution dark field and the selected area diffrac tion patterns we remarkably different. The crystal is quite inhomogeneous with very large grain sites; this can happen for a vu-tcily of reasons (see text). 10/08/2001 15:58 I !I I i 312-986-7822 SCIENCE LIBRARY PAGE 10 390 K. SESHAN chrysotile (Fig. 3). There are also small deformation domains which clearly re semble the UICC standard (B) samples. These fibers are therefore deformed less than the UICC standard samples (Fig. 4), as some intact internal canals can still be seen- It is impossible to derive this conclusion from the brigbt-field range. Samples of heavily deformed chrysotile fiber found in brake drum dust are shown in Fig. 6 in the bright and dark field. Whereas the effects of deformation are not evident in the bright-field image, the difference in the dark-field image is quite striking. The crystal is inhomogeneous. This is reflected in the electron diffraction pattern, now showing a number of spots (Fig. 6c). The mottled contrast of black and bright areas could arise from one of several causes: severe surface deforma tion leading to uneven crystal thickness, conversion (or "grain growth" under heat and deformation) to a large grain polycrystal, or transformation of local areas into a new crystalline phase (e.g., forsterite). Further investigation into carefully deformed chrysotile is required to decide which it is. It is, however, quite clear that these identifying effects are associated only with the samples found in the used brake drum dust. Undeformed and unaltered chrysotile is also found in the brake drum dust collected after use (sample O, Fig. 7). This was confirmed by electron diffraction patterns which were indexed after the camera constant was calibrated using a co-deposited gold standard, with the following results: U>cd brake dun Yada (1967) diameter (A) 2.62 2.34 1.49 diameter (A) 2.60 2.30 1.46 hW 130 220 003 There is also clear dark-field evidence that not all the fibers are deformed. Figure 7 shows the dark- and bright-field images of fibers found in the brake drum dust; the dark-field image resembles that of the UICC chrysotile asbestos (B, shown in Fig. 4) and those in the unused brake lining (C, shown Fig. 5), the "grain sizes" being the same as in the UICC samples. Based upon this observation, it is concluded that a variety of products ranging from almost undeformed to com pletely transformed chrysotile products exist in brake drum dust. DISCUSSION AND CONCLUSIONS It is demonstrated that high-resolution dark-field electron microscopy can dis tinguish the degree of deformation in chrysotile asbestos fibers. In particular, it has been shown that UICC standard chrysotile has undergone microdeformation as a result of ball milling in the preparation step. The dark-field method may then be used by environmental researchers to trace the origins of asbestos fibers. The dark-field images suggest that there are significant changes in the micro structure of chrysotile upon deformation, the cystallographic and microsiructural details of which are complex and are worthy of further study. There are several references to the beam sensitivity of chrysotile (Yada, 1967; Langer et al, 1974). The utility of using this effect to distinguish chrysotile from other non-beam-sensitive materials could be of value to environmental pollution research. I 10/08/200J 15:58 312-598-7822 SCIENCE LIBRARY DEFORMATION OF CHRVSOTILE *SBESW PAGE 11 Ftc. 7- Sample (D): Automobile brake drum duet after u*e () Part field And (b) bright field. This thowi tlai relatively undeformed fibers lUivtve ia the brake drum duet. The grain sizes in the darkfield image* (a) are comparable to those in the burnishing dust (Fig. 5a) or the UICC slotpie* (Fig. 4a), indicating little deformation during use. This preliminary study also shows the need to study details of the growth of the . ebrysotile asbestos and the nature of the defects involved, ifail the diffraction and deformation effects are to be understood. ACKNOWLEDGMENTS I thank G. R. Smith of the Ait Industrial Hygiene Laboratory (AIHL) Berkeley for bringing tWs problem to my attention and preparing (he sampler I acknowledge useful discussions with him and Dr Walter John and thank Professor ). Washburn for encouragement. This work was supported financially by die U.S Energy Research and Development Administration. REFERENCES Aisle, J., Watson, D., aad Bigg, J. (1976). Airborne asbestos in the vicinity of a freeway, Atrooj. Environ, 10, 58V Hatch, D. (1970). Possible alternatives to asbestos as a friction material. Atm. Occup. fiyg. II, 25. Hickish, D. ., and Knight, K L. (1970). Exposure to asbestos during brake maintenance Ann Occup. Hyt II, 17. Hlrsch, P- B., Howie, A., PasMey, D. W,, and Whelan, M. ). (1905). "Electron Microscopy of Thin Crystals." Butterwonhs, London. Lunger, A. M., Mackler, A. D,, and Pooley, F. D. (1974). Electron microscopical investigation of asbestos fiber*. Environ. Health Prnptct 9, 4). Lynch, i. R. (1948) Brake lining decomposition products. /, Air fottut. Control Assoc. 18, 824. Rohi, A N , Langer, A. M,. Wolff, M. S , and Wcisman, I. (1974). Asbestos exposure during brake lining maintenance and repair. Environ. Res. 12,1)0, Seshan, K., and Smith, C. R. (7977), Characterization of chrysolite asbestos in automobUc bmke drum ' 1*0/08/2002 15:58 312-886-7822 f ..... SCIENCE LIBRARY 1 dust toy transmission electron microscopy. "Proceeding* 35tb Annual Meeting of SMSA." Ctairors, Baton Rouge, La, Timtorell, V. (1969). Characteristic* of the irttnutioMl union against cancer standard reference sample* of asbestos, Pneumoconiosis. In "Proceeding* International Conference on Pneumoconiosis, Johannesburg," p, 29 In Oxford Vniv. Pre, England. ' Whittaker, E, J. W, (1366). Diffraction contrast In electron microscopy of Chrysolite, Acre Crystal- (ogr. 21,4416 Yada, K. <1>67). Study of chrysotile asbestos by a high resolution electron microscope. Acta Ctyttol- fogr. 23, 704. Zvyagin, B. B. (1967). "Election-Diffraction Analysis of Clay Mineral Structures'' Plenum. New York. . , ' March 22. 1978 Jo/tc Materials News. 'Page 75 toxic MATERIALS NEWS IN BRIEF ... . . ... Cancer control and prevention hes been largely Ignored by National Institutes'of r- Health,. UCLA.Public Health Dean LeBter Breslow told a national cancer conference re cently, and suggested the government's, cancer prevention program be taken out of Na tional Cancer Institute. "Time after time in the past 25 years the National Instl- tutea of Health has relegated cancer control and disease' control generally to the back vaahea of the. Institutes, failed to seek'adequate funding or take leadership, or literally squeezed It out of the budget,,"-Hreslow said. "Cancer control needs Its-ova strong'advocates;'" . -.> v.'* . ' .'^President Carter, meanwhile, has decreed that'April IS ."Cancer Control Month" .-- a. designation Intended to. educate people: tq '."take, advantage of available resources to . prevent..heedless suffering and death.;,'.-Cause and .prevention research remains one of " our highest priorities." -Carter said^"because prevention offers the best hope for ' ultimate.control .of. cancer-."'".v--T"'v ' ::i National. Cancer: Institute has announced: publication of bioasBay reports on dye . pigment dlarylanlllde yellow'and pesticides- methoxychlor, malathlon. and- trlfluralln. Only trlfluralln was found to be carcinogenic -- in the livers of female mice. All four reports will be available next week from Office of Cancer Communications,. NCI, etheada,. Md..20014. '.. ..'v'-r. \_ = : A{' ' ^idally hazardous, an- ntuced. Seshon hazard esented, and when these fibers are released In the air, they expose repairmen to ightened threats of lung disease and cancer. / ; .. Consumer-Product.Safety Commission would need additional funding of $5-mlllion implement pending legislation ordering safety rules for cellulose insulation, CPSC Chairman John Bylngton told a Senate Appropriations Subcommittee last week. Bylngton also noted that if the agency Is required to deal with various chronic haz- tci'cio identified in an emerging National Cancer Institute study, an additional $5- loilllon and 50 staff positions will be required. Bylngton B6ked that Congress appro priate $3.4-million more for CPSC than the $44.8-milllon President Carter had vccotojaended in his budget. . ' . - ' Occupational Safety and Health Administration has named 11 members to a new standards advisory committee on skin hazards. Committee was formed to identify the occupational exposures in industry which pose s hazard to the skin and to develop a set of guidelines for OSHA to use in drafting a proposed standards on skin hazards. Department of Agriculture's nitrosamlne panel has recommended the department issue a warning that "the.risk of cancer is Increased when fried bacon or the ren dered fst from it are consumed." The panel -called nitrosamines "a potent carcinogen" nod said they-are consistently found In bacon treated in the home. New Jersey's Department' of' Environmental Protection has released preliminary re sults of. a statewide groundwater testing program which is examining 500 wells for selected organic compounds, pesticides and metaic-. DI5& Commissioner Rocco Ricci said early results show that; water quality. In most.^asSx. is-far better than the Federal drinking water standards-,, although 20 violations wete found out of 250 wells. Almost all of the wells contained- traces of some of the che-vleels being sampled, with the majority of well6 contaminated by organic compounds located in heavily populated industrial areas and those contaminated by pesticides more prevalent in agricultural spots. State will similarly test.sir and surface water, DEP said. Justice Department has filed a $20-milllon suit against Outboard Marine Corn.. Waukegan, Mich., charging the firm with discharging 2-million pounds of polychlori nated biphenyls into Waukegan Harbor and bake Michigan. The government asked the court to order the firm to clean up the accumulated PCBs.. Illinois Attorney General's office has filed suit against Amoco Oil Co., and Amoco Pipeline Co. in an attempt to recover more than $838,000 in penalties and dam ages from the companies for two spills of xylene last December. The first 6plll oc curred near Danville when a pipeline transporting the petroleum by-product broke, allowing 700,000 gallons of the substance to leak into the Wabash River. The second spill happened near Bumrick with only a few hundred gallons escaping, hut vapors were ort ofr.y.oaB Ju the area of the spill that, local residents had to be evacuated. ,4* snpl W* PRODUCED BY FORD  V " IMIW .mi ui. XXJL XV t Q GRANTS h CONTRACTS Environmental Protection Agency has awarded University of California. Riverside, $112,000 to study chemical and mode of action of insecticides; Texas ASM Research Foundation. College Station, $85,000 to study baeulovirus pesticides and Identify markers for genetic studies; University of Miami, Coral Gables, Fla., $81,100 to study storage and excretion of halogenated and nonhalogenated organophosphorous pes- ' tlcldes in animals and man; Florida State University, Tallahassee, $36,838 to study high sensitivity FT NMR studies of environmental toxic materials; California Department of Food and Agriculture, Sacramento, $500,000 for Cali fornia's pesticide enforcement program; Nevada Department of Agriculture. Reno, $46,000 for Nevada pesticides enforcement program; Arizona Structural Pest Control Board. Tempe, $37,500 for Arizona pesticides enforcement program plan; Oregon State University. Corvallis, $95,947 to study bioavailability of cadmium from a variety of food-crops potentially grown on land used for sewage sludge disposal; California De partment of Food and Agriculture, Sacramento, $133,580 for certification and imple mentation of pesticide applicator programs in state of California; University of Michigan. Ann Arbor, $33,532 for development of in vitro test sys- tern for evaluation of teratogens; Cryptanalytic Computer Sciences. Inc.. Cherry Hill, N.J., $47,975 to refine, verify and implement the substructural analyses method (SAM) for early-warning toxicity prediction; Interstate Electronics Corp.. Anaheim, Calif., $444,960 for environmental impact statements on ocean dumping sites; Development Planning and Research Associates, Inc.. Manhattan, Kan., $33,903 for development of the economic aspects of guidance for applicants for section 301(c) variances of the Federal Water Pollution Control Act: end North Carolina State University. Raleigh, $72,163 to 6tudy. cytologicsl effects of human exposure to potentially mutagenic en vironmental pollutants. National Institute of Arthritis, Metabolism, and Digestive Diseases has awarded Mason Research Institute, Worcester, Mas6., $59,176 for toxicological evaluation of iron chelators. National Cancer Institute has awarded International Agency for Research on Can cer. Lyon, France, $1,074,151 for evaluation of carcinogenesis risk of chemicals to man; E.G. & G. Mason Research Institute, Rockville, Md., $629,450 for continuation of carcinogenesis bioassay data support system to the bioassay program; and Brandeis University. Waltham, Mass., $126,421 for production and detection of antibodies to chemical carcinogens and other small molecules of interest in cancer research. U.9. Army Medical Research and Development Command h8S awarded Mount Sinai School of Medicine of the City University of New York, New York, N.Y., $110,000 for continuation of research on purification of influenza virus polypeptide antigens and studies of their immunogenicity and toxicity; and Midwest Research Institute, Kansas City, Mo., $260,000 for continuation of research on animal toxicity studies of new drugs. '. *** 13 FR 10474. Meeting April 3-4 in Washington, D.C., of Science Advisory Board's Environmental Health Subcommittee to discuss Teport on pentachlorophenol contaminants. EPA. March 15 FR 10730. . Proposed exemption from tolerance requirement for pesticide chemical sodium chlorate. EPA. March 16 FR 10943. Request for information on occupational exposure to ethylene dibromide. Occupa tional Safety and Health Administration. March 17 FR 11248. Phase-out rules for nonessential aerosol fluorocarbons. EPA. March 17 FR 11301. Permanent standard for occupational exposure to dibromocnloropropane. 0SHA. March 17 FR 11514. .. .. PQki)01 Ookp TPROnUCF.D BY FORD